There are a number of techniques for cutting or severing tubing into lengths. One technique involves the use of a rotary saw but suffers from the disadvantages of slow speed, noise and air pollution due to the generation of shrapnel. A second technique involves a quillotine-type cut using a blade which is driven through the tubing along a diameter thereof. This technique is preferable to the rotary saw from the standpoints of speed, noise and air pollution.
A blade-type cutting mechanism which produces a smooth dimple-free cut of round tubing in a single ram stroke is disclosed in U.S. Pat. No. 4,337,680 issued July 6, 1982. In that mechanism, a notching blade is drawn across the tube to notch a top section thereof prior to the entry of a vertically traveling cutting blade the width of which is sufficient to sever the entire tube.
It is well understood that the blade type tube cutting or severing technique involves the generation of a slug of tubing material representing the volume of the tubing in the path of the severing blade and that the formation and flow of this slug affects the character of the cut. The cutting blade is typically shaped so as to cause the cutting action to move progressively along the leading blade edge or edges to distribute wear and facilitate the flow or slug material. However, at a point part way into the tubing, the angle between a tangent to the blade edge and a tangent of the tube wall at the point of contact is nearly 90.degree. and the power required to continue the cut increases rapidly at this point. This power requirement is increased when the wall thickness of the tubing is relatively great and in some instances the difficulty may be such as to stall the cut off machine. Moreover, the cutting blade wears at a much greater rate in the area of the non-progressive cut and this, in many cases, becomes the limiting factor on blade life.